1. Field of the Invention
This invention relates to the field of ultraviolet-light image recording, and more particularly to methods of recording images with ultraviolet light utilizing photographic elements containing certain white pigments.
2. Description of the Prior Art
In various fields of endeavor involving valuable documents, manuscripts, drawings, etc. which do not readily lend themselves to frequent handling, the preparation of large numbers of copies is made practical by means of photographic intermediates. These intermediates are employed in ultraviolet recording systems such as the diazo process, which uses diazonium salt ultraviolet-light sensitivity for image recording.
Typically, such intermediates are first exposed to form a latent image from line originals, such as engineering drawings, using white light as an exposing source. The latent-image-bearing intermediates are developed to images using common development techniques depending on the particular sensitized emulsion employed. After development, the intermediates are employed as transparencies in the imagewise exposure of ultraviolet-light-sensitive material to ultraviolet radiation, producing the desired copies or "print-outs."
Accordingly, in the foregoing context, intermediates must meet two important photographic requirements. They must be capable of reproducing originals with acceptable line resolution, as perceived by the naked eye. They must also, as developed intermediates, be capable of transmitting ultraviolet light in non-image areas so as to give reasonable exposure times in producing copies.
In the prior art, intermediates of the type containing film support sheets, in addition to at least one emulsion layer sensitive to visible light, fulfill both above requirements. Typically, the film is such material as cellulose ester, glass-filled polyester base, saponified cellulose acetate, vinyl polymers, polycarbonates, and the like. Glassine paper-polyethylene laminates, such as disclosed in U.S. Pat. No. 3,260,602 to Wood et al, are also used for the support but suffer the disadvantages of less acceptable image resolvability. Furthermore, intermediates containing either film or the aforesaid glassine laminate supports are expensive.
Less costly intermediates are available containing paper supports. Common photographic paper support stock is typically used. However, while they are ultraviolet light transmitting, intermediates containing paper supports are less acceptable in their ability to resolve images. Accordingly, it is an objective of this invention to enhance image resolvability of intermediates containing paper supports, without sacrificing reasonable ultraviolet light transmissability requirements.
Usually, when enhanced image resolution is an objective, it is obtained in the art by the addition of functional amounts of highly white-light reflective pigments to a sublayer between the support and the photosensitive emulsion layer. Illustrative examples of such pigments are titanium dioxide, zinc oxide, zinc sulfide, zirconium dioxide, white lead, lead sulfate, lead chloride, lead aluminate, lead phthalate, antimony trioxide, tin oxide, white bismuth, white tungsten and white manganese. Some or all of these materials are also known for other photographic related properties such as emulsion adherence, opacification, reflectance, and stabilization, about which French Pat. Nos. 2,114,360 and 2,099,168, U.S. Pat. No. 3,169,865 and British Pat. No. 1,237,164 are illustrative. There is no suggestion in the art that pigmented elements can, in addition to resolving images, transmit reasonable amounts of ultraviolet light. Furthermore, titanium dioxide, an excellent image-resolving agent, is disadvantageously highly absorbent of ultraviolet light.
It has now been discovered that certain pigmented polyolefin layers give both photographic optical functional requirements when contained within these intermediates. By incorporating effective amounts of zinc sulfide or zirconium dioxide in a polyolefin sublayer between the paper support and the photosensitive emulsion layer, image resolution by high white-light reflectivity is predictably enhanced, and, unexpectedly, the intermediate is ultraviolet-light-transmitting.